1. Field of the Invention
This invention relates to an ignition timing control system for internal combustion engines, more particularly to an ignition timing system for vehicle internal combustion engines that retards the ignition timing during acceleration so as to reduce power shock and avoid the combustion knock that is apt to occur during acceleration.
2. Description of the Prior Art
The increase in engine speed and load that occurs during acceleration of a vehicle internal combustion engine causes the knock zone to shift in the direction of retarded ignition timing, thus increasing the probability of knock occurrence. It has therefore been proposed to prevent the occurrence of knocking during acceleration by employing a technique of ignition timing control for the internal combustion engine which retards the ignition timing during acceleration. For example, Japanese Laid-open Patent Publication No. 57(1982)-99269 proposes a technique of this type which detects engine acceleration from the degree of throttle opening and in response to this detection retards the ignition timing by a prescribed amount so as to avoid the occurrence of knock.
In this prior art system, the adjustment for retarding the ignition timing is carried out directly or immediately after it is detected through the degree of throttle opening that the engine is accelerating. Actually, at the initial stage of acceleration, however, the engine's air intake system experiences a response lag between the change in the throttle pedal depression and the change in the engine load so that the engine output torque does not increase immediately. As a result, the retarding of the ignition timing causes an unnecessary decline in the engine output at the early stage of acceleration. This lowers the feeling of acceleration perceived by the operator and degrades the control response.
In the case of a vehicle equipped with a high-power engine, on the other hand, since the vehicle body is not able to keep up with the sudden change in engine output torque during acceleration, there arises a torque phase lag which is apt to cause vibration of the drive system for conveying the engine output to the drive wheels. This vibration is particularly apt to be manifested as swaying oscillation of the drive shaft. This phenomenon, referred to as power shock, not only degrades the acceleration "feel" but is also undesirable from the point of drivability.